Figure1shows the DTA curves obtained with heating
rate of 20C/min for three alloys. On heating, the first
endothermic peaks belong to the transformations from
martensite to austenite phase, which occur in a temperature
range of 150–200 C, while the second peaks appearing
between 500 and 550C temperatures are related to the
order–disorder solid reactions which are defined as the
transition from ordered b1(DO3-orL21-type structure) to
b(B2) phase [26, 30–33]. Also it has been seen that the
small exothermic energy changes occur at temperatures
close to 650C which are related to the transitions from B2
to A2 [25, 26]. The alloys studied here have not any peaks
related to magnetic transitions because the alloys with Mn
content lower than 8 at% do not exhibit remarkable magnetic properties [26, 32]